Beta limits in long-pulse tokamak discharges
The maximum normalized beta achieved in long-pulse tokamak discharges at low collisionality falls significantly below that observed in short pulse discharges and that predicted by the ideal magnetohydrodynamic (MHD) theory. Recent long-pulse experiments, in particular those simulating the International Thermonuclear Experimental Reactor (ITER) scenarios with low collisionality v(e)*, are often limited by low-m/n nonideal MHD modes. The effect of saturated MHD modes is a reduction of the confinement time by 10%-20%, depending on the island size and location, and can lead to a disruption. The research focuses on a quantitative comparison between both the conventional resistive and neoclassical theories, and the experimental results of several machines which have all observed these low-m/n nonideal modes. This enables us to single out the key issues in projecting the long-pulse beta limits of ITER-size tokamaks and also discuss possible plasma control methods that can increase the soft beta limit, decrease the seed perturbations, and/or diminish the effects on confinement.
Bibliographic Reference: Article: Physics of Plasmas, Vol. 4 (1997) No. 5, pp. 1654-1664
Record Number: 199710931 / Last updated on: 1997-07-23
Original language: en
Available languages: en